Oil sand is essentially comprised of a matrix of bitumen, solid mineral material and water.
The bitumen component of oil sand includes hydrocarbons which are typically quite viscous at normal in situ temperatures and which act as a binder tot the other components of the oil sand. For example, bitumen has been defined by the United Nations Institute for Training and Research as a hydrocarbon with a viscosity greater than 104 mPa s (at deposit temperature) and a density greater than 1000 kg/m3 at 15.6 degrees Celsius.
The solid mineral material component of oil sand typically consists of sand, rock, silt and clay. Solid mineral material may be present in oil sand a coarse mineral material or fine mineral material. The accepted division between coarse mineral material and fine mineral material is typically a particle size of about 44 microns. Solid mineral material having a particle size greater than about 44 microns is typically considered to be coarse mineral material, while solid mineral material having a particle size less than about 44 microns is typically considered to be fine mineral material. Sand and rock are generally present in oil sand as coarse mineral material, while silt and clay are generally present in oil sand as fine mineral material.
A typical deposit of oil sand may contain (by weight) about 10 percent bitumen, up to about 6 percent water, with the remainder being comprised of solid mineral material, which may include a relatively small a mount of impurities such as humic matter and heavy minerals.
Water based technologies are typically used to extract bitumen from oil sand ore originating from the Athabasca area in northeastern Alberta, Canada. A variety of water based technologies exist, including the Clark “hot water” process and a variety of other processes which may use hot water, warm water or cold water in association with a variety of different separation apparatus.
In a typical water based oil sand extraction process, the oil sand ore is first mixed with water to form an aqueous slurry. The slurry is then processed to release bitumen from within the oil sand matrix and prepare the bitumen for separation from the slurry, thereby providing a conditioned slurry. The conditioned slurry is then processed in one or more separation apparatus which promote the formation of a primary bitumen froth while rejecting coarse mineral material and much of the fine mineral material and water. The separation apparatus may also produce a middlings stream from which a secondary bitumen froth may be scavenged. This secondary bitumen froth may be added to the primary bitumen froth or may be kept separate from the primary bitumen froth.
A typical bitumen froth (comprising a primary bitumen froth and/or a secondary bitumen froth) may contain (by weight) about 60 percent bitumen, about 30 percent water and about 10 percent solid mineral material, wherein a large proportion of the solid mineral material is fine mineral material. The bitumen which is present in a typical bitumen froth is typically comprised of both non-asphaltenic material and asphaltenes.
This bitumen froth is typically subjected to a froth treatment process in order to reduce its solid mineral material and water concentration by separating the bitumen froth into a bitumen product and froth treatment tailings.
In a typical froth treatment process, the bitumen froth is diluted with a froth treatment diluent to provide a density gradient between the hydrocarbon phase and the water phase and to lower the viscosity of the hydrocarbon phase. The diluted bitumen froth is then subjected to separation in one or more separation apparatus in order to produce the bitumen product and the froth treatment tailings. Exemplary separation apparatus include gravity settling vessels, inclined plate separators and centrifuges.)
Some commercial froth treatment processes use naphthenic type diluents (defined as froth treatment diluents which consist essentially of or contain a significant amount of one or more aromatic compounds). Examples of naphthenic type diluents include toluene (a light aromatic compound) and naphtha, which may be comprised of both aromatic and non-aromatic compounds.
Other commercial froth treatment processes use paraffinic type diluents (defined as froth treatment diluents which consist essentially of or contain significant amounts of one or more relatively short-chained aliphatic compounds). Examples of paraffinic type diluents are C4 to C8 aliphatic compounds and natural gas condensate, which typically contains short-chained aliphatic compounds and may also contain small amounts of aromatic compounds.
Froth treatment processes which use naphthenic type diluents (i.e., naphthenic froth treatment processes) typically result m a relatively high bitumen recovery (perhaps about 98 percent), but also typically result in a bitumen product which has a relatively high solid mineral material and water concentration.
Froth treatment processes which use paraffinic type diluents (i.e., paraffinic froth treatment processes) typically result in a relatively lower bitumen recovery (in comparison with naphthenic froth treatment processes), and in a bitumen product which has a relatively lower solid mineral material and water concentration (in comparison with naphthenic froth treatment processes). Both the relatively lower bitumen recovery and the relatively lower solid mineral material and water concentration may be attributable to the phenomenon of asphaltene precipitation, which occurs in paraffinic froth treatment processes when the concentration of the paraffinic type diluent exceeds a critical level. This asphaltene precipitation results in bitumen being lost to the froth treatment tailings, but also provides a cleaning effect in which the precipitating asphaltenes trap solid mineral material and water as they precipitate, thereby separating the solid mineral material and the water from the bitumen froth.
Froth treatment tailings therefore typically contain solid mineral material, water, and an amount of residual bitumen (perhaps about 2-12 percent of the bitumen which was contained in the original bitumen froth, depending upon whether the froth treatment process uses a naphthenic type diluent or a paraffinic type diluent).
There are both environmental incentives and economic incentives for recovering all or a portion of the residual bitumen which is contained in froth treatment tailings.
In addition, the solid mineral material which is included in froth treatment tailings typically comprises an amount of heavy minerals. Heavy minerals are typically considered to be solid mineral material which has a specific gravity greater than that of quartz (i.e., a specific gravity greater than about 2.65). The heavy minerals in the solid mineral material which is typically contained in froth treatment tailings may include titanium metal minerals such as futile (TiO2), anatase (TiO2), ilmenite (FeTiO3) and leucoxene (typically an alteration product of ilmenite) and zirconium metal minerals such as zircon (ZrSiO4). Titanium and zirconium bearing minerals are typically used as feedstocks for manufacturing engineered materials due to their inherent properties.
Although oil sand or may contain a relatively low concentration of heavy minerals, it is known that these heavy minerals tend to concentrate in the bitumen froth which is extracted from the oil sand ore, and therefore become concentrated in the froth treatment tailings which result from froth treatment processes, primarily as coarse mineral material. As a result, froth treatment tailings may typically contain a sufficient concentration of heavy minerals to provide an economic incentive to recover these heavy minerals from the froth treatment tailings.
Froth treatment tailings are therefore tailings which are derived from a bitumen froth treatment process. The prior art further includes processes for treating bitumen froth to recover heavy minerals therefrom and processes for treating froth treatment tailings to recover bitumen and/or heavy minerals therefrom. These processes are directed at the treatment of bitumen froth or components of bitumen froth and may therefore be described generally as bitumen froth treatment processes. In addition, these processes typically result in the production of tailings which may be described generally as tailings which are derived from a bitumen froth treatment process.
Canadian Patent No. 861,580 (Bowman) describes a process for the recovery of heavy metals from a primary bitumen froth. Canadian Patent No. 879,996 (Bowman) describes a process for the recovery of heavy metals from a secondary bitumen froth. Canadian Patent No. 927,983 (Penzes) describes a process for the recovery of heavy metal materials from primary bitumen froth. Canadian Patent No. 1,013,696 (Baillie et al) describes a process for producing from froth treatment tailings a quantity of heavy metal compounds such as titanium and zirconium minerals which are substantially free of bitumen and other hydrocarbon substances. Canadian Patent No. 1,076,504 (Kaminsky et al) describes a process for concentrating and recovering titanium and zirconium containing minerals from froth treatment tailings. Canadian Patent No. 1,088,883 (Trevoy et al) describes a dry separatory process for concentrating titanium-based and zirconium-based minerals from first stage centrifuge froth treatment tailings. Canadian Patent No. 1,326,571 (Ityokumbul et al) describes a process for recovering metal values such as titanium and zirconium from froth treatment tailings. Canadian Patent No. 2,426,113 (Reeves et al) describes a process for recovering heavy minerals from froth treatment tailings. Canadian Patent Application No. 2,548,006 (Erasmus et al) describes a process for recovering heavy minerals from froth treatment tailings.
Canadian Patent No. 1,081,642 (Porteous et al) and Canadian Patent No. 1,094,484 (Porteous et al) both describe processes for recovering bitumen from froth treatment tailings. Canadian Patent No. 1,238,597 (Seltzer) describes a process for the recovery of diluent and bitumen from the predominantly aqueous phase of electrostatically treated froth treatment tailings. Canadian Patent No. 1,252,409 (St. Amour et al) describes a method for recovering bitumen from a waste sludge obtained from a retention pond used to store tailings from water extraction of bitumen from tar sands.
Canadian Patent Application No. 2,682,109 (Stay et al) describes a method of extracting a hydrocarbon product from a hydrocarbon-containing stream which comprises adding a first solvent comprising an aromatic solvent to the stream to separate the stream in to a hydrocarbon layer and an aqueous layer, and adding a second solvent comprising a mixture of a polar solvent and a non-polar solvent to the hydrocarbon layer to separate the hydrocarbon product from the hydrocarbon layer.
Froth treatment tailings and other tailings which are derived from a bitumen froth treatment process may also contain an amount of a hydrocarbon diluent which has been used to facilitate the bitumen froth treatment process or processes. For example, a froth treatment diluent may be added to a bitumen froth to facilitate the separation of the bitumen froth into the bitumen product and the froth treatment tailings. Similarly, a hydrocarbon diluent may be added to froth treatment tailings and/or components of froth treatment tailings to facilitate the recovery of bitumen and/or heavy minerals therefrom. It is desirable to recover at least a portion of the hydrocarbon diluent from the tailings so that it can be reused.
Hydrocarbon diluent is typically recovered from froth treatment tailings in a naphtha recovery unit (NRU) in the case of naphthenic type diluents, or in a tailings solvent recovery unit (TSRU) in the case of paraffinic type diluents. Processes relating to the recovery of naphthenic type diluents and paraffinic type diluents from froth treatment tailings are known in the art.
Canadian Patent No. 1,027,501 (Simmer) describes a method for recovering hydrocarbon diluent from hot centrifuge tailings produced in the treatment of bitumen froth which comprises introducing the tailings into a vacuum flash vessel maintained at a sufficiently low sub-atmospheric pressure to vaporize the major portion of the contained diluent.
Canadian Patent No. 2,272,035 (Sarkar et al) describes a method for recovering hydrocarbon diluent from a slurry containing heavy oil, particulate solids, diluent and water which comprises introducing the slurry into a vacuum flash vessel chamber maintained at a sufficiently low sub-atmospheric pressure to vaporize diluent and water and introducing sufficient steam into a pool of residual slurry at the bottom of the chamber to vaporize residual diluent and water.
Canadian Patent No. 2,272,045 (King et al) describes a method for recovering hydrocarbon diluent from tailings produced in the treatment of bitumen froth which comprises introducing the froth treatment tailings into a steam stripping vessel maintained at near atmospheric pressure (the vessel having a plurality of interior, vertically spaced shed decks), evenly distributing the froth treatment tailings over the shed decks to maximize the surface area of the froth treatment tailings, and introducing steam below the shed decks so that it flows countercurrently to the froth treatment tailings and heats the froth treatment tailings to vaporize the hydrocarbon diluent and some water.
Canadian Patent No. 2,353,109 (Foulds et al) describes a process for treating an underflow stream from a last separation step in a paraffinic solvent process for separating bitumen from an oil sands froth which comprises introducing the stream to a solvent recovery vessel that is substantially free of internals and wherein the temperature and pressure are such that the solvent is normally a vapour, maintaining a pool of liquid and solids in the lower part of the vessel at a controlled level for sufficient time to allow the solvent to vapourize, and agitating the pool to a level of agitation where the asphaltenes are dispersed, submerged and re-agglomeration of asphaltenes is inhibited and the solids are maintained in suspension.
Canadian Patent No. 2,587,166 (Sury), Canadian Patent No. 2,613,873 (Sury) and Canadian Patent No. 2,614,669 (Sury) each describe processes for recovering paraffinic solvent from froth treatment tailings which comprises introducing the froth treatment tailings into a tailings solvent recovery unit (TSRU) and introducing inert gas or steam into the TSRU in order to vaporize at least a portion of the paraffinic solvent. In some embodiments, the TSRU contains internals and the inert gas or steam is introduced into the TSRU below the internals. In some embodiments, the TSRU is substantially free of internals and the inert gas or steam is introduced into a liquid pool which is formed in the bottom of the TSRU. In some embodiments, tailings from the TSRU are fed into a second TSRU which is maintained at an absolute pressure which is lower than the first TSRU. In some embodiments, the absolute pressure in the first TSRU is between 100 and 200 kPa and the absolute pressure in the second TSRU is between 20 and 200 kPa. In some embodiments, the froth treatment tailings contain asphaltenes and the paraffinic solvent is vaporized from asphaltene agglomerates.
Canadian Patent Application No. 2,651,155 (Sury et al) describes a method of recovering hydrocarbons from bitumen froth which comprises passing froth treatment tailings to a tailings solvent recovery unit (TSRU) and optionally to a second TSRU, and a third TSRU, wherein the operating pressure in each TSRU is lower than the operating pressure in the preceding TSRU.
Canadian Patent Application No. 2,454,942 (Grant et al) describes a process for separating a diluted tailings into a recovered solvent component and a solvent recovered tailings component which comprises discharging and returning a portion of the solvent recovered tailings component to the solvent recovery apparatus as a returned solvent recovered tailings component.
Canadian Patent Application No. 2,173,559 (Scheybeler) and U.S. Pat. No. 6,712,215 (Scheybeler) each describe a method of recovering solvent from oil sand tailings which comprises directing a stream of tailings and saturated steam through a nozzle and discharging the combined stream of tailings and saturated steam against an impaction target